1. Field of the Invention
The present invention relates to a process for producing a polyolefin resin-coated paper which is used as a photographic support and more particularly to prevention of deterioration in surface quality due to contamination of a die lip which is caused upon preparation of a photographic support by melt-extruding a polyolefin resin composition containing titanium dioxide into a film state and coating such onto at least one surface of a paper sheet or a synthetic paper base.
2. Brief Description of the Prior Art
A polyolefin resin-coated paper for photographic use is already known and a photographic polyolefin resin-coated paper as disclosed in, e.g., U.S. Pat. No. 3,501,298 is obtained by coating both surfaces of a paper base with polyethylene resin, and the polyethylene layer on the emulsion-coated side contains titanium dioxide, blue pigments, fluorescent whitening agents, etc.
However, there is a tendency that needle-like or icicle-like attaches or stains (hereafter simply referred to as "die lip stains") generate at the top of a die lip by extrusion in a short period of time upon melt-extrusion of a polyolefin resin composition containing titanium dioxide, particularly a polyethylene resin composition containing titanium dioxide from a slit die in a film shape and, to be difficult to deal with, there is a tendency that these dye lip stains grow more and more with the passage of time for melt extrusion.
If the dye lip stains generate upon coating by melt-extrusion, streaks are formed on the surface of a photographic support in the longitudinal direction thereof, when the support is prepared in that state, or streakened uneveness in coating is formed due to an uneven coated amount, or stains are sometimes attached and coated onto a film to thereby produce foreign matters. For these reasons, surface quality of a polyolefin resin-coated paper thus prepared is seriously damaged and quite inadequate and of no commercial value for use of a photographic support which requires excellent surface quality.
Further, for completely removing die lip stains once formed, there is nothing but discontinuing the production line and cleaning a die lip; hard labors and time are required for the cleaning and such results in serious reduction in reproducibility. Thus immediate solution of such a problem has been desired.